Data transmitting apparatus, data receiving apparatus and data transmission control apparatus

ABSTRACT

It is objected to simplify a procedure concerning bandwidth acquisition. Bandwidth acquiring means  809  of a second transmitting apparatus  814  acquires a bandwidth which was used by a first transmitting apparatus  806  by using a propagation delay identifier  804  read from first transmitting apparatus  806  and a maximum transmission data size  805  after stopping transmission of first transmitting apparatus  806 . Each apparatus is composed so that transmission is started using this bandwidth and because returning and re-acquisition are not accompanied when the transmission is switched, necessary procedure can be simplified. Further, it is possible to effectively use the bandwidth by using a propagation delay identifier.

This application is a continuation application of application Ser. No.09/586,915, filed Jun. 5, 2000, which is a continuation application ofapplication Ser. No. 08/945,629, filed Apr. 23, 1998 now U.S. Pat. No.6,128,316 which a 371 and is based upon PCT/JP96/01123 filed Apr. 25,1996.

TECHNICAL FIELD

The present invention relates to a transmitting apparatus to transmitvideo and audio signals between digital video/audio apparatuses,acquiring a part of a bandwidth of a transmitting medium beforecommunication.

TECHNICAL BACKGROUND

Nowadays, standardization is proceeded for a bandwidth compressionsystem of a digital video signal and a digital audio signal. The systemis called MPEG (Moving Picture Experts Group) and is divided into twogroups, MPEG1 subject to storage media at a low rate and MPEG2 whichrealizes a high picture quality for broadcast and can correspond todifferent picture sizes. In MPEG2, because compression ratio is variablefor a picture size or a required picture quality, the data size per timeis variable for broadcast programs and contents.

Further, in MPEG2, standardization is also proceeded for datatransmission system used for broadcast. In this transmission system, oneprogram is called stream and the data size is variable in each stream(variable rate) and a system to transmit a plurality of streams alltogether is standardized. Especially, in the case in which a reproducingapparatus to reproduce compressed video audio signals has to isochronizewith the broadcast station which makes compression, like in a case toreceive a broadcast wave, a stream called transport stream is used. Inthis transport stream, a device to make the reproducing apparatuspossible to isochronize is included, using a parameter in the stream. Inthe transport stream, the data is transmitted with a fixed length packet(transport stream packet, hereafter) and data necessary forisochronization is also transmitted with the same kind of packet. It isdescribed in a reference, coding of moving picture and associated audioinformation Part 1, System″ of ISO/IEC International Standard 13818-1,International Technology.

In the case of transmitting a plurality of streams, it is possible tovary the data size per stream if necessary although the bandwidth of theentire transmission medium is fixed. It is possible to effectively usethe bandwidth of the determined transmission medium by allocating abroad bandwidth to a stream which a high rate is required andsuppressing the rates of the other streams, not equally sharing thebandwidth of the entire transmission medium to each stream.

On the other hand, in the case in which broadcast signal is oncereceived, a specific stream is selected and is transmitted or recordedagain, a bandwidth for transmission or recording has to be secured onthe basis of the maximum rate in the selected stream. For such apurpose, a method indicating a buffer for smoothing a stream (smoothingbuffer, hereafter) and a bandwidth necessary for transmission orrecording with a reading rate from the smoothing buffer (leak rate,hereafter) is adopted in MPEG2. The smoothing buffer memory size and theleak rate are shown by parameters included in the stream.

In the method using smoothing buffer and leak rate, the received streamis once stored in a smoothing buffer memory and is read from here at theleak rate. As long as a smoothing buffer memory having a size expressedby a parameter in the stream and a leak rate are used, the smoothingbuffer memory is guaranteed not to overflow. Therefore, in the case ofbeing transmitted or recorded again, transmission or recording becomespossible by securing the bandwidth equal to the leak rate. Because byonce smoothing the rate, it becomes unnecessary to secure the bandwidthequal to the maximum rate which rarely occurs, the bandwidth attransmitting or recording the stream with a variable rate can be minimumand it is possible to effectively use a transmitting medium or recordingmedium.

However, because timing information of each transport stream packet isdeteriorated by once storing the stream in a smoothing buffer memory,the reproducing apparatus of video and audio signals cannot isochronize.Therefore, in the case of transmission or recording, timing informationwritten in the smoothing buffer memory is added to each packet. On theother hand, at the receiving or reproducing apparatus, the timinginformation is reproduced by once storing each transport stream packetin a packet having the same size as a smoothing buffer memory andoutputting the output based on timing information added to eachtransport stream packet and as a result, it becomes possible toisochronize at the reproducing apparatus of video and audio signals.

Thus, in order to transmit a MPEG2 transport stream, it is necessary tobe able to reproduce the timing of each transport stream packet in thereceiving apparatus of the transport stream packet. As such atransmission medium which can reproduce the timing, there is P1394interface. P1394 is a high speed serial interface for the nextgeneration multimedia which is studied at IEEE. It is described in thereference, High Performance Serial Bus P1394/Draft 7.1v1″.

P1394 is a transmitting medium of serial bus type and all nodesconnected to a bus have isochronized timing information. When atransport stream packet of MPEG2 is transmitted, the timing of eachtransport stream packet is secured using the timing information.

An apparatus connected to P1394 (node, hereafter) is connected in a treestructure having branches and a node having a plurality of terminalsrelays the signal by outputting a signal received from one of theterminals to another terminal. Accordingly, it is secured to arrive toevery node connected with data outputted from any node. As a result,P1394 works as a bus theoretically although it has a tree structure.

However, because P1394 realizes a bus by relaying a plurality of nodes,there occurs a propagation delay depending on the number of relayingnodes as well as a propagation delay determined by the length of thetransmission medium. Further. in P1394, it is secured that a pluralityof nodes do not simultaneously transmit, by that only one node assignsbuses.

Thus, an identifier to identify the node (node ID, hereafter) is addedto each node composed as a bus. The addition of the node ID isautomatically done by initializing a bus generated when a new node isadded to the bus or on the contrary, when a node is separated from thebus (bus reset, hereafter). When a bus reset is generated, a nodeconnected to the bus outputs a packet indicating a connection state ofthe node (self ID packet, hereafter) to the bus according to apredetermined order. The node ID is determined by the output order ofthe self ID packet and the self ID packet includes the node IDdetermined at outputting to the self ID packet and information whetherthe other nodes are connected to each terminal or not. As for the nodeon the bus, the tree structure composing the bus can be known byreceiving and analyzing all of self ID packets outputted from each node.

In P1394, two kinds of transfer, a isochronous transfer used fortransferring the data which is necessary of real time such as a MPEG2transport stream or a digital video signal and an asynchronous transferused for outputting data which is unnecessary of real time are possible.P1394 works on the basis of every 125 microsecond period (cycle,hereafter) and is used for isochronous transfer at a first half of eachcycle and for asynchronous transfer at a second half.

When a isochronization transfer is done, time,(bandwidth) used duringone cycle is acquired in the node controlling the bandwidths beforecommunication. P1394 has a node controlling bandwidth used withisochronous transfer and a bandwidth to be used is acquired from thebandwidth controlling node. The node to execute a isochronous transfercan transfer the data in a range of the acquired bandwidth and the datatransmitted with isochronous transfer is outputted as a packet specifiedby P1394. In a isochronous transfer, it is possible to transfer realtime data by secure the transfer of the data size predetermined at everycycle.

The bandwidth to be acquired before transmission is a summation ofoverhead parts such as a bandwidth necessary for transferring the datain practice and a bandwidth necessary for transferring the data addedfor propagation delay generated at data transfer and error detection. InP1394, it is possible to use mixture of a plurality of transmissionrates and outputs signals directing their transmission rates foridentification before packet transmission.

Moreover, apart from MPEG2, a digital VCR for converting video and audiosignals into digital data and recording is being developed. In thisdigital VCR system, a digital video signal is compressed and recorded ina tape. Signal compression method for a high definition (HD, hereafter)television picture as well as standard definition (SD, hereafter)television picture is also being developed. The compressed data size ofan HD video signal is twice as much as that of an SD video signal andeach is always compressed to data having a fixed rate, different fromMPEG.

Because the digital VCR signal is a compressed signal, if it istransmitted after being once restored into an analog video signal and isconverted into a digital signal again, picture quality deteriorationoccurs. Therefore, a digital VCR signal is desired to transmit as adigital signal and P1394 can be used also for a transmission of digitalVCR data.

On the other hand, in P1394, every node connected to a bus have animaginary address space and asynchronous data transfer between nodes isexecuted as reading and writing of the address space. In a part of theaddress space, a register used for controlling the working of each nodeis included. In the node connected to a bus, the node state can be knownby reading out from a control register of another node and on thecontrary the node can be controlled by writing to the control register.

It is thought to control transmission and reception of the isochronousdata, using such a control register. In such a case, a transmissionstate or a reception state can be known by reading a register forisochronous communication control. On the other hand, it is possible tocontrol to start or stop transmission or reception of the isochronousdata by writing a required value into the register.

When a MPEG2 transport stream is transferred using a transmitting mediumto communicate after acquiring a bandwidth before transmission, likeP1394, it is thought that the data rate changes on the way of transferand a bandwidth necessary for transfer exceeds the bandwidth alreadyacquired. Its example is the case in which the leak rate varies into alarge value by a change of a program during transfer. On the other hand,when digital VCR data is transferred, it is thought that the signalchanges from an SD video signal to an HD video signal on the way oftransfer. Its example is the case in which an SD video signal isrecorded halfway of the tape and after that the recorded signal changesinto an HD video signal. When the tape is playbacked, the signal changesfrom SD video data to HD video data on the way of playback and the datasize changes to twice. Thus, when the data rate changes, transmissionexceeding a previously acquired bandwidth could be done.

As an example, there is a case using P1394 in a transmitting medium.When a MPEG2 transport stream is outputted to P1394, a bandwidth isacquired based on a leak rate of the stream outputted beforetransmission and is outputted. However, when the leak rate changes to alarge value on the way of transfer, a bandwidth necessary for outputtingexceeds the already acquired bandwidth and there could be a risk tooutput data more than that corresponding to the previously acquiredbandwidth to a bus. On the other hand, when the signal changes from anSD video signal to an HD video signal and the data size increases twice,there is a risk to output twice data of that corresponding to thepreviously acquired bandwidth to the bus.

In P1394, when data exceeding the data corresponding to the previouslyacquired bandwidth is supplied to a bus, time required for transmittingdata which must transmit during one cycle for isochronous communicationexceeds the predetermined and assigned time for isochronous transfer.When such a bandwidth overflowing occurs, asynchronous communication cannot be done because the time for asynchronous communication is short.Moreover, when the time required for isochronous data communicationexceeds 125 microseconds, the bus becomes impossible to work and notonly the data to be a cause but also all isochronous data flowing on thebus can not continue transmission and reception.

As explained above, when a transmitting medium which acquires a part ofa bandwidth of the transmitting medium before transmission is used andtransmission is done exceeding the acquired bandwidth, there is aproblem to interfere the other communications using the sametransmitting medium.

On the other hand, the apparatus receiving data through a transmittingmedium could receive an incorrect data when the rate of the transmitteddata changes to a large value. A first example is the case that the leakrate changes to a large value when a MPEG2 transport stream is receivedfrom a transmitting medium and video and audio signals are reproducedfrom the received data or the transport stream is recorded. A secondexample is the case that the digital VCR data changes from an SD videodata to an HD video data when the digital VCR data is received from thetransmitting medium and video and audio signals are reproduced orrecorded from the received data. In such a case, because the bandwidthnecessary for data transmission exceeds the acquired bandwidth in thetransmitting medium bandwidth, the transmitting apparatus can notcontinue a normal transmission and as a result, an incorrect data couldbe transferred to the transmitting medium.

When a transport stream or VCR data received at the receiving apparatusis reproduced or recorded, in the case in which an imperfect transportstream or an imperfect digital VCR data is received or the received datais lost, it happens to reproduce or record an incorrect data. Moreover,in the case in which the receiving apparatus is working, synchronizingwith a sync signal included in the received data, the isochronizationcould loose and malfunction could occur.

Thus, in the case in which data is received from a transmitting mediumwhich acquires a part of the bandwidth of transmitting medium beforetransmission and communicates and when the bandwidth necessary for thedata transfer exceeds the bandwidth which previously acquired in thetransmitting medium bandwidth, incorrect data could be supplied to thetransmitting medium and when the incorrect data is supplied to thetransmitting medium, the apparatus which is receiving this data inducesmalfunction. It is a problem.

On the other hand, like P1394, in the case in which transmission is doneafter acquiring a part of transmitting medium bandwidth beforetransmission, the other apparatuses could commence outputting, stoppingthe already starting communication and using the bandwidth which hasbeen used in the stopped communication.

An example is the case in which while a first apparatus is outputtingdata to a transmitting medium, a second apparatus tries to startoutputting data. When a bandwidth in which the second apparatus canoutput the data is left in the transmitting medium, the second apparatuscan start outputting after acquiring the bandwidth. However, if thenecessary bandwidth is not left, it can not start transmitting.Accordingly, the transmission can be started after the second apparatussecures the bandwidth necessary for outputting, making the firstapparatus stop to output.

In such a case, it is necessary to start transmission after the controlnode once returns the bandwidth which has been used and acquires again.Because the bandwidth has to be acquired after returning the bandwidth,the apparatus to acquire the bandwidth has to confirm if the bandwidthreturning is finished and keep watch on the returning action. Moreover,because it takes time from returning the bandwidth to acquiring itagain, it has a risk that another node acquires the bandwidth. That is,there is a problem that a procedure necessary for acquiring thebandwidth is complex.

On the other hand, when a propagation delay depending on a connectionform of the node connected to a transmitting medium occurs like P1394, abandwidth has to be acquired including an overhead such as thepropagation delay time, in addition to a bandwidth necessary for actualtransmission.

In such a case, it is possible to acquire a bandwidth based on maximumpropagation delay time. However, if the bandwidth to be acquired isdetermined on the basis of an assumed maximum propagation delay time,because an extra bandwidth which is actually unnecessary is acquired,the transmitting medium can not be effectively utilized and therefore,there is a risk to prevent the other communications which are originallyto be able to communicate. That is, if the bandwidth is acquired basedon the maximum value of propagation delay, there is a problem not to beable to effectively use the transmitting medium.

In a usual transmission apparatus, when information concerning smoothingbuffer memory and leak rate is given in the data, it is necessary toanalyze the data and extract information concerning the rate in order todetermine the transmission bandwidth or the recording mode and there isa demerit that the hardware size at recording of the receiving apparatusbecomes large.

Moreover, if the buffer at the receiving apparatus side overflows orunder flows, the data transmission becomes impossible and usually it cannot be controlled at the transmission apparatus.

DISCLOSURE OF THE INVENTION

To solve the problems described above, a data transmitting apparatus inaccordance with a first invention is a transmitting apparatus totransmit, after acquiring a part of the bandwidth which a transmittingmedium has, before transmission and is characterized by including:

bandwidth detection means for detecting a bandwidth of data inputted tothe transmitting apparatus;

necessary bandwidth calculation means for calculating a necessarybandwidth at the transmitting medium from the bandwidth outputted fromthe bandwidth detection means;

transmission condition judge means for comparing the necessary bandwidthoutputted from the necessary bandwidth calculation means and theacquired bandwidth acquired from the transmitting medium bandwidth andjudging whether the necessary bandwidth exceeds the acquired bandwidthor not;

transmission control means for outputting the data only while the judgeresult outputted from the transmission condition judge means indicatesthat the necessary bandwidth does not exceed the acquired bandwidth; and

transmission means for outputting the data outputted from thetransmission control means to the transmitting medium.

A data transmitting apparatus in accordance with a second invention is atransmitting apparatus to transmit, after acquiring a part of thebandwidth which a transmitting medium has, before transmission and ischaracterized by including:

bandwidth detection means for detecting a bandwidth of data inputted tothe transmitting apparatus;

necessary bandwidth calculation means for calculating a necessarybandwidth at the transmitting medium from the bandwidth detected at thebandwidth detection means;

transmission condition judge means for comparing the necessary bandwidthoutputted from the necessary bandwidth calculation means and theacquired bandwidth acquired from the transmitting medium bandwidth andjudging whether the necessary bandwidth exceeds the acquired bandwidthor not;

transmission control means for outputting the data only while the judgeresult outputted from the transmission condition judge means indicatesthat the necessary bandwidth does not exceed the acquired bandwidth;

bandwidth information adding means for adding the bandwidth outputtedfrom the bandwidth detection means to the data outputted from thetransmission control means as bandwidth information and outputting onlythe bandwidth information while the data is not inputted from thetransmission control means; and

transmission means for outputting the data outputted from the bandwidthinformation adding means and added with the bandwidth information to thetransmitting medium.

A data receiving apparatus in accordance with a third invention ischaracterized by that a transmitting apparatus acquiring a part of thebandwidth of a transmitting medium before communication and,transmitting only while the bandwidth of data to be transmitted does notexceed the acquired bandwidth, provides with:

reception means for receiving the data outputted to the transmittingmedium from the transmitting medium;

transmission stop detection means inputting the data received by thereception means and for detecting that the transmitting apparatus stopsoutputting by detecting that the data does not arrive for a specifiedperiod; and

processing means for processing to respond according to the detectedresult which the transmission stop detection means detects.

A data receiving apparatus in accordance with a fourth invention ischaracterized by that a transmitting apparatus acquiring a part of thebandwidth which the transmitting medium has, before communication,transmitting the data added with the bandwidth information while thebandwidth of the transmitted data does not exceed the acquiredbandwidth, and transmitting only the bandwidth information when thebandwidth of the data exceeds the acquired bandwidth provides with:

reception means for receiving the data added with the bandwidthinformation outputted to the transmitting medium from the transmittingmedium;

transmission stop detection means inputting the data received by thereception means and for detecting that the transmitting apparatus stopsto output the data by detecting that the data does not arrive for aspecified period;

bandwidth information separation means inputting the data added with thebandwidth information received at the reception means and for separatingthe added bandwidth information from the data and outputting it; and

processing means for processing to respond according to at least one ofthe detected result which the transmission stop detection means detectsand the bandwidth information separated at the bandwidth informationseparation means.

A data transmitting apparatus in accordance with a fifth invention is adata transmitting apparatus in which a propagation delay occursdepending on a connection topology of the apparatus connected to thetransmitting medium and a part of the bandwidth which the transmittingmedium has is acquired before transmission and which is connected to akind of transmitting medium to transmit provides with:

propagation delay identifier holding means for holding a propagationdelay identifier determined by a connection topology of the apparatusconnected to the transmitting medium; and

maximum transmission data size holding means for holding a maximumtransmission data size indicating a maximum size of the data which canhold in a packet outputting to the transmitting medium;

and is characterized by that the propagation delay identifier holdingmeans can read and write the propagation delay identifier through thetransmitting medium and the maximum transmission data size holding meanscan read the maximum transmission data size through the transmittingmedium.

A data transmission control apparatus in accordance with a sixthinvention is what connected to a transmitting medium in which apropagation delay occurs depending on a connection topology of theapparatus connected to the transmitting medium and is determined by aconnection topology of the apparatus connected to the transmittingmedium and is a control apparatus for a transmission apparatus havingpropagation delay identifier holding means to hold a propagation delayidentifier expressing propagation delay size of the transmitting mediumand is characterized by providing with:

analyzing means for analyzing the connection topology of the apparatusconnected to the transmitting medium;

identifier determining means for determining the propagation delayidentifier according to the analysis result outputted from the analyzingmeans; and

identifier setting means for setting the propagation delay identifierdetermined by the identifier determining means in the propagation delayidentifier holding means.

A data transmission control apparatus in accordance with a seventhinvention is characterized by that in a data transmission controlapparatus in accordance with a sixth invention, the analyzing means havea function to judge the connection form according to the maximum numberof relay apparatuses assumed from the number of apparatuses connected tothe transmitting medium.

A data transmitting apparatus in accordance with an eighth invention ischaracterized by providing with:

measurement means for measuring the data size arrived in a specifiedfixed period;

bandwidth determination means for determining the transmission bandwidthfrom the data size measured at the measurement means; and

transmission means for transmitting according to the transmissionbandwidth determined at the bandwidth determination means.

A data transmitting apparatus in accordance with a ninth invention ischaracterized by providing with:

judge means for judging whether a transmission packet which thereceiving apparatus receives from the transmission medium has passed thetiming to be outputted from the receiving apparatus or not;

a counter for counting up the value when the transmitting apparatustransmits one piece of the transmission packet and counting down thevalue when the judge means judges that each transmission packet haspassed the timing to be outputted from the receiving apparatus;

determination means for determining the transmission timing of eachtransmission packet so that the value counted at the counter does notexceed a certain fixed value; and

transmission means for transmitting the digital data according to thetransmission timing determined at the determination means.

A data transmitting apparatus in accordance with a tenth invention is atransmitting apparatus for transmitting the digital data inputted atevery packet and is characterized by providing with:

calculation means for calculating a delay time from the buffer capacityprovided in the receiving apparatus and the data rate of the digitaldata inputted to the receiving apparatus;

judge means for comparing the delay time with a specific value andjudging;

transmission time stamp adding means for adding the input time to thereceiving apparatus and the output of the judge means to eachtransmission packet as a transmission time stamp which is timinginformation which the receiving apparatus is to output the packet; and

transmission means for transmitting the packet added with thetransmission time stamp.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a block diagram of essential parts of a transmitting apparatusfor transmitting data and a receiving apparatus for receivingtransmitted data in accordance with an exemplary embodiment of thepresent invention.

FIG. 2 shows a packet used when data is transmitted using a isochronoustransfer of P1394 in accordance with an exemplary embodiment of thepresent invention.

FIG. 3 shows each field structure of CIP header included in a data fieldof a packet used in a isochronous transfer of P1394 in accordance withan exemplary embodiment of the present invention.

FIG. 4 is a block diagram of an essential part of a transmittingapparatus for transmitting isochronization data in accordance with anexemplary embodiment of the present invention.

FIG. 5 shows a bandwidth necessary to acquire when isochronization dataof P1394 is transmitted in accordance with an exemplary embodiment ofthe present invention.

FIG. 6 shows a connection of the nodes apart by (N−1) pieces of relaynodes in N time connections in accordance with an exemplary embodimentof the present invention.

FIG. 7 shows a construction of PCR which is a register to controltransmission of the isochronization data in accordance with an exemplaryembodiment of the present invention.

FIG. 8 is a block diagram of essential parts of two transmittingapparatuses when transmission nodes of the isochronization data areswitched in accordance with an exemplary embodiment of the presentinvention.

FIG. 9 is a block diagram of essential parts of a transmission controlapparatus for determining and setting a propagation delay identifier anda transmitting apparatus in which the propagation delay identifier isset in accordance with an exemplary embodiment of the present invention.

FIG. 10 is a block diagram of a first example of a bandwidth detectionmeans in accordance with an exemplary embodiment of the presentinvention.

FIG. 11 is a block diagram of a second example of a bandwidth detectionmeans in accordance with an exemplary embodiment of the presentinvention.

FIG. 12 is a block diagram of a data processing means in accordance withan exemplary embodiment of the present invention.

FIG. 13 is a block diagram of a transmission timing determiner inaccordance with an exemplary embodiment of the present invention.

FIG. 14 shows a structure of a transmission time stamp in accordancewith an exemplary embodiment of the present invention.

THE PREFERRED EXEMPLARY EMBODIMENT OF THE PRESENT

Exemplary embodiments of the present invention are explained below,referring to the drawings.

A first exemplary embodiment of the present invention is shown in FIG.1. In the first exemplary embodiment, a transmitting apparatus 124 totransmit data 108 to a transmitting medium 114 includes data processingmeans 130 for processing, for example, converting data 108 to betransmitted into a transmitting format by division or combination;bandwidth detection means 101 for detecting the bandwidth of the data108; necessary bandwidth calculation means 102 for calculating thenecessary bandwidth in transmitting medium 114 from a data bandwidth 109detected at bandwidth detection means 101; transmission condition judgemeans 103 for comparing necessary bandwidth 110 calculated at necessarybandwidth calculation means 102 with acquired bandwidth 104 acquiredfrom the bandwidth which transmitting medium 114 has, beforetransmission, judging a transmission condition and outputting a judgedresult 111; transmission control means 105 inputting the Judged resultand for outputting the data outputted from data processing means 130 asdata 112 to be transmitted according to the judged result; bandwidthinformation adding means 106 for adding data bandwidth 109 outputtedfrom bandwidth detection means 101 to data 112 outputted fromtransmission control means 105 as bandwidth information and outputtingit; and transmission means 107 for transmitting data 113 added withbandwidth information outputted from bandwidth information adding means106 to transmitting medium 114. Transmitting apparatus 124 is what iscomposed as a part of a receiver for digital television broadcast or adigital VCR and data 108 inputted to transmitting apparatus 124 is datareceived at a tuner 126 or data reproduced at a playback apparatus 127.As the data 108, a signal such as a MPEG2 transport stream or data of adigital VCR is inputted.

A receiving apparatus 125 for receiving data outputted from transmittingapparatus 124 through transmitting medium 114 includes reception means115 for receiving data from transmitting medium 114 and outputting;transmission stop detection means 116 for inputting data 119 received atreception means 115, detecting that a specified time data does notarrive and outputting detected result 120; bandwidth informationseparation means 117 for inputting data 119 added with the bandwidthinformation received at reception means 115, separating bandwidthinformation 121 and outputting; and processing means 118 for inputtingdetected result 120 outputted from transmission stop detection means116, inputting bandwidth information 121 from bandwidth informationseparation means 117 and processing to respond according to theseinputs. Receiving apparatus 125 is what is composed as a part of adigital VCR or a television receiver and a received data 122 is suppliedto an apparatus such as a recording apparatus 128 or a reproducingapparatus 129.

As a transmitting medium 114 used for transmission and reception ofdigital video and audio data, P1394 interface can be used.

When data 108 supplied to transmitting apparatus 124 is a MPEG2transport stream inputted from tuner 126 or playback apparatus 127, anecessary bandwidth for outputting to transmitting medium 114 iscalculated and acquired from a parameter indicating leak rate includedin the transport stream, before transmission. In the case of P1394,receiving apparatus 125 receiving data from transmitting medium 114 andthe other apparatuses connected to the same bus as well as transmittingapparatus 124 can acquire the bandwidth and the bandwidth used for datatransmission is acquired from a node to control the bandwidth. When theapparatus to acquire the bandwidth is other than transmitting apparatus124, a leak rate of the stream is previously inquired to transmittingapparatus 124, a necessary bandwidth is acquired based on the leak rateobtained as the result and transmission is requested for transmittingapparatus 214. The inquiry of the leak rate or the direction of thetransmission can be done through asynchronous communication using thesame bus. The bandwidth to be acquired here is what indicates time usedin one cycle at data transmission and what a necessary bandwidth formaking a packet at transmission to P1394 described later is added to thebandwidth which the leak rate indicates.

While transmitting apparatus 124 is transmitting a transport stream,bandwidth detection means 101 detects a leak rate included in thetransport stream and outputs as a bandwidth data 109 of the dataoutputted to transmitting medium 114. Necessary bandwidth calculationmeans 102 which received the bandwidth data 109 of the data transmittedfrom bandwidth detection means 101 calculates the stream actually usedat outputting to a P1394 and outputs as a necessary bandwidth 110 byadding such as a necessary bandwidth data for making a packet attransmission to the leak rate, in a similar way to acquiring thebandwidth before starting transmission.

Transmission condition judge means 103 holds an acquired bandwidth 104acquired before transmission, compares it with a necessary bandwidth 110inputted from necessary bandwidth calculation means 102 and outputs as ajudged result 111. Transmission control means 105 inputting the judgedresult 111 outputs a transport stream inputted to transmitting apparatus124 when the judged result 111 is showing that necessary bandwidth 110is smaller than acquired bandwidth 104 because the transmission isthought to be able to continue without any trouble and on the otherhand, the stream inputted to transmitting apparatus 124 is deleted whenthe judged result 111 is showing that necessary bandwidth 110 is largerthan acquired bandwidth 104 because continuing transmission couldprevent the other isochronous transfer or asynchronous transfer.

Bandwidth information adding means 106 is supplied with a transportstream 112 from transmission control means 105 and adds bandwidth data109 which is the data supplied from bandwidth detection means 101 asbandwidth information and outputs it. At this time, while transmissioncontrol means 105 stops outputting the transport stream, only thebandwidth information is outputted. Transmission means 107 inputtingtransport stream 112 and bandwidth information 109 makes transportstream 112 a packet and transmits it to transmitting medium 114. Apacket structure of a isochronous transfer of P1394 is shown in FIG. 2.

The packet used when the digital video and audio data are transferredusing P1394 is composed of a packet header 201 used for discriminate thekinds of the packets, CRC (Cyclic Redundancy Check) 202 for the packetheader added for detecting the error at the packet header at signalreception, a payload part 207, and CRC 205 for the data added fordetecting error at the payload part. Payload part 207 is composed of CIP(Common Isochronous Packet) header 206 used for adding the kind of dataor the bandwidth information, a plurality of data blocks 204 includingvideo and audio data. Data 108 inputted to transmitting apparatus 124 iscalled source packet and is transmitted, being included in a part of thepayload part 207 as it is or being divided. as a data block having afixed size.

CIP header 206 is composed of 4 byte data 203 a including parameterconcerning data transfer method and 4 byte data 203 b including kinds ofdata and parameter necessary for each kind. A detailed structure of CIPheader 206 is shown in FIG. 3. The CIP header is composed of a SID(Source node Identification number) 301 which is a identifier foridentifying the node transmitting the data; DBS (Data Block Size) 302showing a data block size; FN (Fraction Number) 303 indicating how thesource packet was divided or not divided to make a data block; QPC(Quadlet Padding Count) 304 indicating the number of bytes supplied tothe source packet in order to adjust the source packet size and divide;SPH (Source Packet Header) 305 indicating whether the source packet hasa header based on the kinds of data or not; DBC (Data Block continuityCounter) 306 which is a counter for confirming continuity of the datablock; FMT (Format) 307 indicating kinds of transmitted data; and FDF(Format Dependent Field) 308 including parameter necessary for each kindof data.

When transmission means 107 transmits a transport stream to P1394, it isindicated by FMT 307 that the signal is a MPEG2 transport stream and thebandwidth information showing a leak rate is transmitted as a part ofFDF 308. As for the other fields, CIP header 206 is composed, includinga suitable value and is outputted as a isochronous transfer packet. Inthis case, if the data which transmission means 107 receives frombandwidth information adding means 106 is a transport stream, a datablock is made from the transport stream and a parameter indicating theleak rate is transferred as a part of FDF 308. On the other hand, if thedata supplied by bandwidth information adding means 106 is onlybandwidth information, a parameter indicating the leak rate is includedin a part of FDF 308 and only the CIP header is transmitted as payloadpart 207, because there is no transport stream to be transmitted.

Therefore, when the bandwidth of transport stream inputted totransmitting apparatus 124 is larger than the previously acquiredbandwidth 104, the transport stream can be stopped to output and it canbe prevented to disturb to continue isochronous transfer andasynchronous transfer to the other apparatuses using the same bus.Moreover, because the packet of only CIP header is always transmittedeven while the data is not transmitted, the receiving apparatus whichreceived the packet can process corresponding to it. If it is a packetnot including a transport stream, identification information of thetransmitting apparatus is included in SID 301 and it is transferred toFMT 307 and FDF 308 that the data to be transmitted is a MPEG2 transportstream and the parameter indicating the leak rate of the stream.

On the other hand, in receiving apparatus 125 receiving a packet fromtransmitting medium 114, reception means 115 receives a packet forisochronous transfer from P1394 after confirming the packet header anddata 119 added with bandwidth information is outputted after confirmingthe continuity of the data block by using CIP header. Transmission stopdetection means 116 which has received data 119 detects thattransmitting apparatus 124 stopped transmission by the information thatthe transport stream has not arrived and outputs a detection result 120.In the MPEG2 transport stream, because the maximum interval amongtransport stream packets included in the stream is determined, when thetransport stream is not received beyond this maximum interval, it can,be judged that transmitting apparatus 124 has stopped to transmit. Evenwhile the transport stream is not received, it can be confirmed that thetransmitting medium is correctly working because the packet includingonly the CIP header is received. On the other hand. when the packet isnot received at all, it can be thought that the transmitting medium ortransmitting apparatus 124 is not correctly working.

bandwidth information separation means 117 is inputted with the data towhich the bandwidth information supplied from reception means 115 isadded, separates into bandwidth information 121 and data 122 and outputsthem separately. When the data supplied from reception means 115 is onlybandwidth information, bandwidth information 121 is outputted. Thetransport stream included in data 122 outputted from bandwidthinformation separation means 117 is recorded at a recording apparatus128 or reproduced into video and audio signals at reproducing apparatus129.

Processing means 118 processes based on detection result 12O suppliedfrom transmission stop detection means 116 and bandwidth information 121supplied from bandwidth information separation means 117. When detectionresult 120 indicating transmission stop of transmitting apparatus 124 isinputted, processing means 118 directs to stop the works, becauseneither recording apparatus 128 can give a correct recording action norreproducing apparatus 129 can give a normal reproducing action.

When an effective transport stream is not supplied from transmittingmedium 114, because neither there is data for recording or reproducingnor isochronization information included in the transport stream isgiven, the isochronization of the receiving apparatus is disturbed andmalfunction could be occur. When transmitting apparatus 124 stopsoutputting the transport stream, processing means 118 directs to stoprecording and reproducing actions and worthless recording andreproducing actions can be prevented and malfunction is also prevented.

Processing means 118 is supplied with bandwidth information 121 frombandwidth information separation means 117 and watches the leak rate ofthe transport stream under reception. Recording apparatus 128 recordinga transport stream can determine the rate at recording based on the leakrate of the transport stream. While recording is made receiving thetransport stream, if the leak rate of the transport stream underreception comes to exceed the recording rate, it becomes not to continuea correct recording. Therefore, processing means 118 outputs a signal123 to direct recording to recording apparatus 128 and can continuerecording action by stopping recording or varying the recording rate atrecording apparatus 128.

Even a packet not including a transport stream, because identificationinformation of transmitting apparatus 124 can be obtained from the SIDvalue included in the CIP header, it is possible to direct transmittingapparatus 124 to stop transmission and when the apparatus which acquireda bandwidth of transmitting medium 114 is receiving apparatus 125 andtransmitting apparatus 124 is stopping transmission as a result of thatthe leak rate varies and the necessary bandwidth exceeds the acquiredbandwidth, it becomes possible that receiving apparatus 125 acquires alacked bandwidth and makes transmitting apparatus 124 start to transmitagain.

When data 108 supplied to transmitting apparatus 124 is digital VCR datasupplied from playback apparatus 127, the bandwidth necessary fortransmitting to transmitting medium 114 is calculated and acquiredbefore transmission, depending on which the kind of video signal is anSD video signal or an HD video signal. Because the digital VCR data isdata having a fixed rate, it is possible to determine the bandwidthbased on the kind of video signal. Similar to a MPEG2 transport stream,the other apparatuses than the apparatus to transmit can also acquirethe bandwidth. In this case, the kind of transmitted video signal ispreviously inquired.

When transmitting apparatus 124 is transmitting the digital VCR data,bandwidth detection means 101 detects whether the kind of video signalis an SD video signal or an HD video signal and outputs bandwidthinformation 109 of the data necessary for outputting to transmittingmedium 114. Necessary bandwidth calculation means 102 which has receivedbandwidth information 109 which is transmitting data from bandwidthdetection means 101 adds the bandwidth which is necessary according tomaking a packet at transmission or the like to the data bandwidth, in asimilar way to acquiring the bandwidth before starting transmission andthe bandwidth actually used at outputting the data to P1394 iscalculated and is outputted as a necessary bandwidth 110.

transmission condition judge means 103 holds acquired bandwidth 104acquired before transmission, compares it with necessary bandwidth 110supplied from necessary bandwidth calculation means 102 and outputsjudged result 111. Because it is thought that it gives no trouble tocontinue transmission when judged result 111 is smaller than occupiedbandwidth 104, transmission control means 105 inputting judged result111 outputs the digital VCR data inputted to transmitting apparatus 124.On the other hand, because continuing transmission could prevent theother isochronous or asynchronous transfer when necessary bandwidth 110is larger than acquired bandwidth 104,transmission control means 105deletes the inputted data to transmitting apparatus 124.

Bandwidth information adding means 106 inputs the digital VCR data fromtransmission control means 105 and adds the bandwidth information whichis the data supplied from bandwidth detection means 101 as bandwidthinformation and outputs it. In this case, while transmission controlmeans 105 stops outputting the data, it outputs only bandwidthinformation. Transmission means 10, inputting the digital VCR data andbandwidth information supplied from bandwidth information adding means106 is made into a packet and is outputted to transmitting medium 114.

The packet for isochronous transfer used on P1394 in this case has thesame structure as a packet used for transferring a MPEG2 transportstream. When transmission means 107 transmits digital VCR data to P1394,it is indicated to be digital VCR data by FMT 307, information which thevideo signal is an SD video signal or an HD video signal is transmittedas a part of FDF308. Because the digital VCR data has a fixed rate, ithas the same effect as expressing the data bandwidth by identifyinginformation which an SD video signal or an HD video signal is. As forthe other fields, CIP header 206 is composed including an appropriatevalue and is transmitted as a packet for isochronous transfer. In thiscase, at transmission means 107, when the data received from bandwidthinformation adding means 106 is data added with the bandwidthinformation, a data block is made from the digital VCR data andparameter expressing a kind of video signal is transferred as a part ofFDF 308. On the other hand, when the data received from bandwidthinformation adding means 106 is only bandwidth information, theparameter expressing a kind of video signal is included in a part of FDF308 and only a CIP header is transmitted as payload part 207 because ofno data to transmit.

Thus, because the data of digital VCR data inputted to transmittingapparatus 124 changed from an SD video data into an HD video data, ifthe bandwidth necessary for transmission becomes larger than thepreviously acquired bandwidth 104, the transmission of the digital VCRdata can be stopped and it can be prevented to disturb to continueisochronous or asynchronous transfer of the other apparatuses using thesame bus. Moreover, similar to the case of transport stream transfer,because the packet of only the CIP header is always transmitted, thereceiving apparatus receiving this packet can process correspondingly.Even if it is a packet not including data, identification information ofthe transmitting apparatus is included in SID 301 and it is transferredto FMT 307 and FDF 308 that the data to transmit is digital VCR data andinformation which the data is an SD video data or an HD video data.

At receiving apparatus receiving a packet from transmitting medium 114,transmission means 115 receives a packet for isochronous transfer fromP1394 after confirming a packet header and outputs digital VCR data 119to which bandwidth information is added after confirming continuity ofthe data block, using CIP header. Transmission stop detection means 116receiving data 119 detects that transmitting apparatus 124 has stoppedtransmission from no arriving of the data for a previously determinedperiod and outputs detection result 120. Similarly to receiving atransport stream, it can be confirmed that the transmitting medium iscorrectly working even if for a period the data is not received becausethe packet including only CIP header is received. On the other hand,when the packet is not received at all, it is thought that thetransmitting medium or transmitting apparatus 124 is not correctlyworking.

Bandwidth information separation means 117 is supplied data to whichbandwidth information is added from reception means 115, separates intobandwidth information 121 and data 122 and outputs them separately. Whenthe data received from reception means 115 is only bandwidthinformation, only bandwidth information 121 is outputted. The digitalVCR data outputted from bandwidth information separation means 117 isrecorded at recording apparatus 128 or reproduced into video and audiosignals at reproducing apparatus 129.

Processing means 118 processes the data based on detection result 120supplied from transmission stop detection means 116 and bandwidthinformation 121 supplied from bandwidth information separation means117. When detection result 120 directing transmission stop totransmitting apparatus 124 is inputted, because recording apparatus 128can not correctly record and also reproducing apparatus 129 can notcorrectly reproduce, processing means 118 directs to stop these actions.

When effective digital VCR data is not received from the transmittingmedium, because not only there is no data for recording or reproducingbut also isochronization information transferred together with the datais not received, the receiving apparatus could loose isochronization andmalfunction could occur. When transmitting apparatus 124 stopstransmission of the data, processing means 118 directs to stop recordingand reproducing and worthless recording and reproducing as well asmalfunction can be prevented.

Processing means 118 inputs bandwidth information 121 from bandwidthinformation separation means 117 and watches which kind of digital VCRdata the signal under reception is. Recording rate of recordingapparatus 128 has to be decided depending on the kind of digital VCRdata. When the receiving data changes from an SD video signal to an HDvideo signal or vice versa while it is recording the receiving data,correct recording becomes impossible. Recording can be continued bydirecting to stop recording or to change the recording rate to recordingapparatus 128.

Even if it is a packet not including digital VCR data, because theidentification information of transmitting apparatus 124 can be obtainedfrom the SID value included in the CIP header, when transmittingapparatus 124 is directed to stop transmission or an apparatus acquiringthe bandwidth of transmitting medium 114 is receiving apparatus 125 andthe kind of data changes to another kind and transmitting apparatus 124stops transmission due to that the necessary bandwidth exceeds theacquired bandwidth, receiving apparatus 125 supplements an insufficientbandwidth and thus, transmitting apparatus 124 becomes to be able tostart transmission again.

The variation of the bandwidth necessary for such a transmission isthought to occur when the transmitting data varies from a MPEG2transport stream to digital VCR data or vice versa. Even when such akind of data varies, transmitting apparatus 124 becomes to be able tostart transmission again by comparing the necessary bandwidth attransmission with the bandwidth acquired from the transmitting mediumand judging a transmitting condition.

Because it can know a kind of data from the CIP header included in thereceiving packet, receiving apparatus 125 can vary a recording method ofrecording apparatus 128 when the receiving data changes from a MPEG2transport stream to digital VCR data or vice versa or can stop recordingif the newly received data cannot recorded. In such a case, it ispossible to stop reproducing when a corresponding reproducing method isswitched or newly received data can not be reproduced. Moreover, when anapparatus directing data transmission is a receiving apparatus 125 andthere is no need of continuing communication because the received datacan not be recorded nor reproduced, it is possible to directtransmitting apparatus 124 to stop transmission.

Even it has no bandwidth information adding means 106 and bandwidthinformation separation means 117, transmitting apparatus 124 preventfrom transmitting over the acquired bandwidth and it is possible toprevent to disturb continuing isochronous and asynchronous communicationother than communication using the same transmitting medium 114.Receiving apparatus 125 detects the stop of transmission fromtransmitting apparatus 125, stops recording and reproducing and canprevent malfunction.

A construction of bandwidth detection means and data processing means isdescribed below.

FIG. 10 is a first example of a block diagram of bandwidth detectionmeans.

Bandwidth detection means 101 is composed of a information table holder1 and a transmission rate information extractor 2.

The inputted transport stream packet header of MPEG2 is analyzed andinformation tables such as a programming mapping table (PMT) and anevent information table (EIT) are extracted and held at an informationtable holder 1. Program names, broadcast time, rate information and thelike are written in these tables.

Information about transmission rate, for example smoothing bufferdescriptor in the PMT is extracted at transmission rate informationextractor 2. The transmission bandwidth is determined based on theextracted information at necessary bandwidth calculation means 102.

FIG. 11 is a second example of a block diagram of bandwidth detectionmeans. This is used when transport stream packet of MPEG2 has notransmission rate information or when the analyzing load in the data isdesired to reduce. The block 3 is a counter and the block 4 is abandwidth determiner in bandwidth detection means 101 shown in FIG. 11.

Counter 3 counts the data size (here, the number of data packets) oneafter another. supplied to the transmitter during a fixed period, forexample, a period as long as 24.576 MHz which is a working clock of IEEE1394. Because the data packet size is a fixed number, that is 188 bytesin MPEG2 transmission, it is comparatively easy to find an average rate.

Bandwidth determiner 4 can catch the average rate per period from thevalue counted by counter 3. The average rate is selected one from aplurality of transmittable bandwidths which the transmitter has. Atdetermination of the transmission bandwidth, transmission bandwidthdeterminer 5 selects the narrowest transmission bandwidth, considering arate which is larger by a fixed rate (for example, 1.2 times) than theaverage rate caught at bandwidth determiner 4 and within a range whichcan absorb jitter due to deviation of data arrival timing and the like.To secure the selected transmission bandwidth, a transmission packetincluding bandwidth secure request information is transmitted to thetransmission medium.

The rata rate can be directly known by the above operation withoutanalyzing inside the signal of MPEG2 and the transmission bandwidth canbe easily determined using it. The information concerning the determineddata rate can be transmitted by newly writing in the table.

FIG. 12 shows a block diagram of data processing means. In dataprocessing means 130, the block 21 is a smoothing buffer, the block 22is an arrival timing catcher, the block 23 is a time stamp generator,the block 24 is a time stamp adder, the block 25 is a transmissiontiming determiner, the block 26 is a cycle time register (CTR) and theblock 27 is a transmission packet converter.

The time stamp of the transmission is generated based on the countedvalue of CTR 26 which is a clock set the time among the apparatusesconnected to the transmission medium. Arrival timing when each transportstream packet of MPEG2 is supplied from tuner 126 or playback apparatus127 is outputted from a decoder box of MPEG2 or the like to thetransmitting apparatus is acquired at arrival timing catcher 22. Timestamp generator 23 latches the value of CTR 26 at arrival timing andgenerates transmission time stamp, adding the counted value of themaximum delay time between the designated transmitting apparatus andreceiving apparatus. Transmission time stamp is added at the top of thedata block. An example of the format is shown in FIG. 14.

The inputted transport stream packet is added with the transmission timestamp and is converted into a data block at time stamp adder 24 afterbeing stored at smoothing buffer 21 and then is converted into atransmission packet in which a plurality of data blocks gather attransmission packet converter 27. The transmission packet is sometimesconverted after dividing into some data blocks by the rate or the like.

FIG. 13 shows a block diagram of a transmission timing determiner 25.The block 30 is an output time judging unit, the block 31 is a counterand the block 32 is a transmission timing controller. The timingactually transmitted from transmission packet converter 27 to thetransmission medium is controlled at transmission timing determiner 25.

Output time judging unit 30 is supplied with time stamp value indicatingthe output time at the receiver of each data packet from time stampgenerator 23 and holds them and then, compares each time stamp valuewith the present CTR value and judges if the data packet was alreadyoutputted from the receiver.

The CTR values of the receiving apparatus and the transmitting apparatusare the same because they are set so as to be equal against every nodeconnected. Therefore, the above judgment is enough only comparingbetween two values.

Counter 31 counts down one by one for a data packet and counts up one byone at every time when a data packet is transmitted from transmissionpacket converter 27 when output time judging unit 30 judges to bealready outputted″. That is, the counted value becomes the same as thenumber of data packets in the buffer of the present receiver.Transmission timing controller 32 outputs a signal to control the outputtiming from transmission packet converter 27 according to the outputfrom counter 31. That is, when the count value becomes large and almostbecomes to exceed a fixed value (concretely, the ratio of buffersize/data packet size), the output from transmission packet converter 27to the transmission means is delayed. When the counted value approacheszero, the output from transmission packet converter 27 to thetransmission means is advanced. Controller 32 can be composed of amicrocomputer and software or the like according to the above concept.

According to the above process, transmission timing determiner 25 can becontrolled at the transmission apparatus so that the buffer at thereceiving apparatus side does neither overflow nor under flow. Thereceiving apparatus can output a signal to a recording apparatus and thelike with a correct timing, without overflowing of the buffer in thereceiving apparatus, by outputting the signal with a timing described inthe transmission time stamp. The counted value is controlled so as to beas large as possible within a range not to exceed the above fixed value.By this control, the number of data packets in the receiver bufferbecomes maximum without overflowing and it becomes possible not tointerrupt the output in the receiving apparatus as many as possible whensome trouble occurs in the receiving apparatus or on the transmissionmedium and the transmission packet does not arrive in the receivingapparatus for a certain period.

In the second exemplary embodiment, data transmitting apparatus 407transmitting isochronous data to transmitting medium 408 shown in FIG. 4is composed of a propagation delay identifier holding means 401 holdinga propagation delay identifier 405, maximum transmission data sizeholding means 402 holding a maximum transmission data size 406,bandwidth occupying means 403 and transmission/reception means 404.

FIG. 5 shows a necessary bandwidth to acquire when transmittingisochronous data to P1394. The bandwidth of the isochronous data is abandwidth corresponding to a time determined by a total time of time T1from detecting that the bus is not yet used to requesting ownership, atransmission time T2 necessary for that the request of the ownership ofbus arrives at the control node, a judge time T3 at the control node ofownership of bus, a transmission time T4 necessary for receiving a judgeresult outputted from the control node of ownership, an occupying periodT5 of the bus before data transmission, time T6 for outputting a signalindicating transmission rate of the data, time T7 necessary fortransmitting a packet itself, time T8 for outputting a signal indicatingtransfer finish and a propagation delay time T9 necessary for that thepacket arrives at the node controlling ownership of bus.

In this bandwidth, the value other than T7 which is a time necessary fortransferring the packet itself is independent of transmission rate andtransmitting data size and is determined by the number of relay nodesexisting between the transmitting node and the node controlling theownership of bus. In P1394, because there is no need that the nodecontrolling the ownership of bus exists on the center of the connection,time exceeding the packet transfer time is different from node to node.In order to obtain time for each node, the location of the nodecontrolling ownership of bus on the bus must be considered.

However, when this time is obtained as a value independent of thelocation of the control node of ownership and the same value is used forevery node connected to the bus, it is good that the number of maximumrelay nodes existing in the bus is used as the number of maximum relaynodes between the transmission node and the node controlling ownershipof bus.

Therefore, considering that transmission node 603 apart from node 601controlling ownership of bus by (N−1) pieces of relay node 602 with Ntimes of connection as shown in FIG. 6 outputs a packet and using thevalue indicated in the standard of P1394, the time Toh used for otherthan packet transfer is expressed by Eq. 1.

Toh=(1.797+N×0.494) microseconds  (Eq. 1)

Expressing this value by a unit used for bandwidth control in P1394, thebandwidth BWoh necessary for other than packet transferbandwidth(overhead bandwidth, hereafter) can be expressed by Eq. 2.

BWoh=88.3+N×24.3  (Eq. 2)

The unit of the bandwidth used in P1394 is a value regarding a bandwidthnecessary for transferring a 2 bit signal at transfer speed of 100 Mbpsas 1.

Propagation delay identifier 405 is obtained from a connection topologyof the apparatus connected to transmitting medium 408 and the overheadbandwidth can be determined as only one value by the value of thisidentifier. Propagation delay identifier 405 held in propagation delayidentifier holding means401 is determined at an initial condition, basedon the number of maximum connections allowed for the used transmittingmedium.

When the used transmitting medium is P1394, value corresponding to anoverhead bandwidth having 15 relay nodes with 16 times of connections isset. On the other hand, maximum transmission data size 406 held inmaximum transmission data size holding means 402 expresses the maximumdata size which can be included in a payload part which is a data partof a packet for isochronous communication used at P1394. Maximumtransmission data size 406 used here expresses what is equivalent toacquired bandwidth 104 described in the first exemplary embodiment.

The packet format used in a isochronous data transmission is the sameformat as that shown in FIG. 3 of the previous exemplary embodiment. Thesizes and the number of data blocks included in the payload part aredetermined by kind and rate of the transmitted data.

Data of 20 bytes including packet header is added to the packet inaddition to the isochronous data. Among these, what is held in maximumtransmission data holding means is a summation of 8 bytes of CIP header206 and the data size of the isochronous data. Accordingly, thebandwidth necessary for acquisition before transmission is a summationof a bandwidth necessary when a packet having a size which 12 bytes areadded to the maximum transmission data size is transmitted at a rateused for transmission and the above-mentioned overhead bandwidth.

FIG. 7 shows a composition of a transmission PCR (Plug Control Register)which is a register for controlling isochronous data transmission and islocated in an address space which each node of P1394 has. The PCR is a32 bit register and is composed of a 1 bit on-line identifier 701indicating if the PCR is usable, a 1 bit broadcast connection counter702 indicating that transmission controlled by the transmission PCR canstop during transmission, a 6 bit point-to-point connection counter 703indicating the number of apparatuses which directed the PCR, a 2 bitunused field 704, a channel 705 indicating a channel number used fortransmission of 6 bit isochronous data, a 2 bit data rate 706 indicatinga rate used for transmission, a 4 bit overhead ID 707 corresponding topropagation delay identifier holding means, and a 10 bit payload size708 corresponding to maximum transmission data size holding means andexpressing the payload size by a unit of 4 bits.

In the first exemplary embodiment, payload size 708 of the PCR can beused as an acquired bandwidth 104.

The transmission control apparatus to control transmission can controltransmission by writing values in the register and can know atransmission condition at that time by reading the values in theregister. The transmitting apparatus executes transmission when a valueother than zero is written in broadcast connection counter 702 orpoint-to-point connection counter 703, while on-line identifier 701 oftransmission PCR is 1. On the contrary, when both are 0, the outputtingis stopped. Only when point-to-point connection counter 703 is 0 andbroadcast connection counter 702 is 1, the apparatuses other than theapparatus directed start of transmission clear up broadcast connectioncounter 702 and can stop the transmission.

Because propagation delay identifier 405 could have been changed to adifferent identifier by a reason mentioned later when bandwidthacquiring means 403 acquires the bandwidth, the bandwidth is acquiredbased on propagation delay identifier 405 held in propagation delayidentifier holding means 401 and maximum transmission data size 406 heldin maximum transmission data size holding means 402. When the bandwidthis acquired, bandwidth acquiring means 403 reads maximum transmissiondata size 406 from maximum transmission data size holding means 402 andadds 12 bytes to maximum transmission data size 406 and acquires thebandwidth necessary for transmitting a packet of this size at data rate706 included in the PCR, to obtain a packet size from the payload sizeby the reason mentioned above. Bandwidth acquiring means 403 readspropagation delay identifier 405 from propagation delay identifierholding means 401 and adds the overhead bandwidth determined bypropagation delay identifier 405 to the bandwidth for packettransmission.

Bandwidth acquiring means 403 outputs the bandwidth acquired from theabove result to transmission/reception means 404 as a request forbandwidth assignment and transmission/reception means 404 outputs thereceived request for bandwidth assignment to transmitting medium 408 asan asynchronous packet to send a bandwidth control node. As the requestresult, the received packet is outputted to bandwidth acquiring means403. Bandwidth acquiring means 403 judges if the bandwidth was acquiredfrom the request result for bandwidth assignment. Transmission start canbe directed by writing in broadcast connection counter 702 of PCR orpoint-to-point connection counter 703, based on the result of acquiringthe bandwidth.

Concerning the above procedure, an example of bandwidth assignmentaiming transmission of digital VCR data which is now under developmentis explained below.

When the digital VCR data is transmitted using P1394, the data isdivided at every 480 bytes and is transferred as a isochronous packet.Accordingly, the value of 122, which 488 bytes is expressed as a unit of4 bytes, is written as a maximum transmission data size, where the valueof 488 bytes is a value which 8 bytes of CIP header is added to thedividing unit of 480 bytes.

Bandwidth acquiring means 403 reads out the value 122 which is a maximumtransmission data size from maximum transmission data size holding means(payload size 708) included in PCR and multiplies it by 4 times and itis known that the payload size is 488 bytes. Further, it is found outthat the value 500 bytes added with 12 bytes to 488 bytes is a size of apacket for isochronization data. Still further, a bandwidth necessaryfor a packet transmission is found based on the value of data rate 706included in PCR. The bandwidth becomes 2000, using a bandwidth unit usedin P1394 when data rate 706 is indicating a transfer at 100 Mbps. On theother hand, the bandwidth becomes 1000, which is a half of 2000 whendata rate 706 is indicating a transfer at 200 Mbps.

Bandwidth acquiring means 403 reads out a propagation delay identifierfrom propagation delay identifier holding means (overhead ID 707)included in the PCR. Bandwidth acquiring means 403 has a correspondencetable of overhead pattern versus bit pattern of a 4 bit propagationdelay identifier shown in Table 1 and the overhead bandwidth is foundfrom the propagation delay identifier read out.

TABLE 1 propagation delay identifier overhead bandwidth 0000 113 0001137 0010 162 0011 166 0100 210 0101 235 0110 259 0111 283 1000 307 1001332 1010 356 1011 380 1100 405 1101 429 1110 453 1111 477

The summation of the overhead bandwidth obtained as a result and thevalue 2000, which is a packet bandwidth is an acquired bandwidth.

When point-to-point counter 703 of the PCR is 0 and broadcast connectioncounter 702 is 1, because the transmission can be stopped by that theother nodes than that directs to start transmission clears broadcastconnection counter 702, a different transmission can be made by usingthe bandwidth used in the stopped transmission. At this time, the usedbandwidth is known from the propagation delay identifier included in thePCR and the maximum transmission size.

A block diagram of a transmitting apparatus at such a switching oftransmission is shown in FIG. 8. In FIG. 8, a first transmittingapparatus 806 which is now transmitting is composed of propagation delayidentifier holding means 801 holding a propagation delay identifier 804,maximum transmission data size holding means 802 holding a maximumtransmission data size 805, and transmission/reception means 803transmitting and receiving a packet between transmission/reception means803 itself and transmitting medium 807. A second transmitting apparatus814 which newly starts transmission is composed oftransmission/reception means 808 transmitting and receiving a packetbetween transmission/reception means 808 itself and transmitting medium807, bandwidth acquiring means 809, propagation delay identifier holdingmeans 810 holding a propagation delay identifier 812, and maximumtransmission data size holding means 811 holding a maximum transmissiondata size 813.

When second transmitting apparatus 814 stops transmission of firsttransmitting apparatus 806 and transmits using the bandwidth which firsttransmitting apparatus 806 was using, broadcast connection counter ofthe PCR of first transmitting apparatus is cleared. At this time,bandwidth acquiring means 809 of second transmitting apparatus reads outpropagation delay identifier 804 held in propagation delay identifierholding means 801 composed as a part of the PCR of first transmittingapparatus 806 and maximum transmission data size 805 held in maximumtransmission data size holding means 802.

In this case, because the node ID of first transmitting apparatus 806 isincluded in the CIP header of the packet for isochronous data which hasa composition shown in FIG. 3 and is transmitted by the firsttransmitting apparatus, second transmitting apparatus 814 can specifythe node ID of first transmitting apparatus 806 which is transmittingthe data by once receiving the data which is now being transmitted andchecking the CIP header.

Thus, bandwidth acquiring means 809 of second transmitting apparatus 814looks for the bandwidth which the first transmitting apparatus acquiredand was using in a similar way to the above-mentioned usual bandwidthacquiring way based on propagation delay identifier 804 and maximumtransmission data size 805 read out from first transmitting apparatus806. The bandwidth found here, which has been acquired by firsttransmitting apparatus 806, can be used by second transmitting apparatus814 after first transmitting apparatus 806 stops transmission.

Although the data rate used when the bandwidth used by firsttransmitting apparatus 806 is found is usually used reading out datarate 706 included in the PCR, because it can be known from the receptionrate when a packet for isochronous data is received in order to know thenode ID of first transmitting apparatus 806, it is not always necessaryto read out data rate 706 included in the PCR.

Bandwidth acquiring means 809 compares the given bandwidth acquired bythe above procedure with the bandwidth which is similarly acquired frompropagation delay identifier 812 held in second transmitting apparatus814 and maximum transmission data size 813 held in maximum transmissiondata size holding means 811 and is planned to use and when there is anydifference between the given bandwidth and the bandwidth planned to useit is necessary to return an extra bandwidth to the control node of thebandwidth or on the contrary, an insufficient bandwidth is newlyacquired.

In this case, when propagation delay identifier 804 readout from firsttransmitting apparatus 806 is smaller than propagation delay identifier812 held in propagation delay identifier holding means 810 of secondtransmitting apparatus 814,propagation delay identifier 812 of secondtransmitting apparatus 814 can be made to have the same value aspropagation delay identifier 804 read out from first transmittingapparatus 806. This is because the propagation delay identifier is foundonly from the connection topology of the bus and the minimum propagationdelay identifier among them can be used if it is a node connected to thesame bus, although a different value could be written at every nodeaccording to a calculation method used when the propagation delayidentifier mentioned later is calculated.

As mentioned before, the initial value of the propagation delayidentifier holding means is a value corresponding to the case the bushas a maximum composition allowed by P1394 standard. Therefore, secondtransmitting apparatus 814 which is given a bandwidth has an initialvalue as a propagation delay identifier 812 and on the other hand,propagation delay identifier 804 of first transmitting apparatus 806 caneffectively use the bandwidth which the transmitting medium has bycomparing which value is smaller and adopting the smaller one when thebandwidth is given in the case when a smaller value than the initialvalue is written, by checking the connection topology of the bus.

FIG. 9 shows a block diagram of a procedure when a transmission controlapparatus founds a propagation delay identifier. In the exemplaryembodiment, a transmitting apparatus 910 is composed oftransmission/reception means 907 for transmitting and receiving a packetto and from a transmitting medium 906 and propagation delay identifierholding means 908 for holding a propagation delay identifier 909. Atransmission control apparatus 905 is composed of analyzing means 901for analyzing a connection topology of the apparatuses connected to atransmitting medium, identifier determination means 902 for determiningpropagation delay identifier according to the analysis result,identifier setting means 903 for setting propagation delay identifier909 in propagation delay identifier holding means 908 of transmittingapparatus 910, and transmission/reception means for transmitting andreceiving a packet to and from transmitting medium 906.

Analysis means 901 receives all of the self ID packets outputted fromeach node connected to the bus at the reset of P1394 and analyzes a treestructure of the bus, using the information included in the self IDpackets. BY analyzing the tree structure, the number of relay nodes whencommunication is made between any two of the nodes is found and themaximum value is outputted. On the other hand, identifier determinationmeans 902 calculates a maximum propagation delay which could occur fromthe maximum number of relay nodes at the bus inputted from analyzingmeans 901 and finds the size of the overhead bandwidth necessary toacquire at isochronous data transmission based on this value. Identifierdetermination means 902 determines which the most appropriatepropagation delay identifier is from the overhead bandwidth and outputsit.

As the correspondence between the number of relay nodes and the overheadbandwidth used in this case, for example, the values shown in Table 2can be used.

TABLE 2 the number of relay nodes overhead bandwidth 0 113 1 137 2 162 3166 4 210 5 235 6 259 7 283 8 307 9 332 10 356 11 380 12 405 13 429 14453 15 477

The values shown in Table 2 are maximum values determined independent ofthe location of the node controlling the ownership of bus and arecalculated using Eq. 2. It is also possible to calculate a propagationdelay, considering the location of the node controlling the ownership ofbus on the bus. In this case, even if the maximum number of relay nodesexisting on the bus is the same, the value could be a smaller than anoverhead bandwidth shown in Table 1. The values shown in Table 1 areused for the response between overhead bandwidths and bit patterns of 4bit propagation delay identifiers. The propagation delay identifier canbe determined like the above.

Thus, identifier determination means 902 obtains the overhead bandwidthfrom the maximum number of relay nodes supplied from analyzing means 901and determines the propagation delay identifier from the overheadbandwidth and outputs it. The overhead bandwidth can be determined inonly one value from the propagation delay identifier by determining sucha correspondence.

Identifier setting means 903 receives a propagation delay identifierdetermined at identifier determination means 902 and writes inpropagation delay identifier holding means 908 of transmitting apparatus910. The writing is done by writing procedure to the PCR, using anasynchronous packet.

As mentioned above. an identifier determined by a maximum connectiontopology allowed for P1394 is written as an initial value in propagationdelay identifier holding means 908 of transmitting apparatus 910. Tochange this value. it is necessary to analyze the connection topology ofthe bus and know the maximum number of relay nodes. However, because aisochronous data communication is possible even if the propagation delayidentifier is used as it is an initial value without analyzing theconnection topology of the bus, not all transmitting apparatuses have toprovide with analyzing means 901 of connection topology, identifierdetermination means 902 or identifier setting means 903. In this case,because a larger bandwidth than an originally necessary bandwidth isacquired, it is impossible to effectively use the bandwidth which thetransmitting medium has.

It becomes possible to efficiently use the bandwidth which thetransmitting medium has by connecting transmission control apparatus 905to the transmitting medium finding a propagation delay identifier byanalyzing the connection topology of the apparatuses connected to thebus, and setting a propagation delay identifier which is thoughtappropriate for propagation delay identifier holding means of thetransmitting apparatus connected to the bus. Because propagation delayidentifier holding means can write through a bus, if there is at leastone transmission control apparatus on the bus, it is possible to set asmaller propagation delay identifier than the initial value and as aresult, not all transmitting apparatuses have to provide with analyzingmeans 901 of connection topology, identifier determination means 902 orthe like and it becomes possible to effectively use the bandwidth whichthe transmitting medium has by only having a correspondence tablebetween propagation delay identifiers and overhead bandwidths shown inTable 1.

A transmission control apparatus other than the transmitting apparatuseshaving a propagation delay identifier holding means could write moreappropriate propagation delay identifiers than the value already set.Accordingly, when the bandwidth acquiring means acquires the bandwidthas mentioned above, it is necessary to read a value at propagation delayidentifier holding means and find an overhead bandwidth based on theread value.

Further, the propagation delay identifier held in propagation delayidentifier holding means has to be the value used when the bandwidth wasacquired, for using at switching transmitting apparatuses. Accordingly,a transmitting apparatus which a propagation delay identifier is set bythe transmission control apparatus is restricted only to thetransmitting apparatus which does not transmit at the time. That is, apropagation delay identifier can be set only when both broadcastconnection counter 702 of the PCR and point-to-point connection counter703 are zero.

The most appropriate value of a propagation delay identifier isoriginally determined in one value when the connection topology of thebus is determined. However, to find the most appropriate value, theconnection topology of the bus is analyzed and all the number of relaynodes between nodes and in some cases, the location of the control nodeof the ownership of bus on the bus have correctly to be obtained. Acomplex analyzing process is required to do such a processing. Whenthere are few apparatuses connected to the bus, the propagation delayidentifier can be set to a smaller value than the initial value onlybased on the number of apparatuses which may not be the mostappropriate.

In P1394, it is decided by a standard that the number of relay nodesbetween the farthest nodes must be 15 and the number of connection timesmust be 16. When the number of nodes M connected to the bus is smallerthan 17, the number of relay nodes between the farthest nodes neverexceeds (M−2) whatever connection topology is taken. Accordingly, insuch a case, the connection topology is not analyzed and the propagationdelay identifier can be determined, regarding (M−2) which is the maximumnumber of relay nodes of the number of nodes connected the bus as thenumber of relay nodes. When M is larger than 17, the value 15 which isthe maximum value of the values allowed for P1394 is used. By setting apropagation delay identifier obtained like the above, it becomespossible to effectively use the bandwidth comparing with the casepropagation delay identifier is not set at all, without taking a complexprocess, although the bandwidth which the transmitting medium has cannot be used to the full.

Thus, there could be a plurality of methods by which a transmittingapparatus finds a propagation delay identifier and there could be aplurality of transmission control apparatuses to set propagation delayidentifiers on the same bus. Accordingly, in propagation delayidentifier holding means in which a propagation delay identifier whichis thought to be the most appropriate is written, a larger propagationdelay identifier than that is sometimes written. In such a case, itcould be dangerous that the bandwidth which the transmitting medium hascan not be effectively used. The above problem can be prevented bysetting a propagation delay identifier only when it is smaller than thevalue already set, comparing a value now trying to set with the valuealready set.

AVAILABILITY IN THE INDUSTRIAL FIELD

In the first invention, data transmission is stopped by that the databandwidth inputted to a transmitting apparatus changes when thebandwidth necessary for outputting to a transmitting medium exceeds thebandwidth acquired before communication and as a result, it is possibleto prevent to disturb a continuous communication of the otherapparatuses using the same transmitting medium.

In the second invention, data transmission is stopped by that the databandwidth inputted to a transmitting apparatus changes when thebandwidth necessary for outputting to a transmitting medium exceeds thebandwidth acquired before communication and as a result, it is possibleto prevent to disturb a continuous communication of the otherapparatuses using the same transmitting medium and in addition to this,it is possible to inform the bandwidth necessary for data transmissionto a receiving apparatus by transmitting the data bandwidth to betransmitted even while the data transmission is stopped and apparatuseswhich received the data can work using this bandwidth information.

In the third invention, a state of transmission stop at the transmittingapparatus is detected and a corresponding process at the receivingapparatus can be done by detecting that any data is not received for adesignated period, when the data is received from the transmittingmedium.

In the fourth invention, a state of transmission stop at thetransmitting apparatus is detected and a corresponding process at thereceiving apparatus can be done by detecting that any data is notreceived for a designated period, when the data is received from thetransmitting medium and in addition to this, it is possible to do acorresponding process based on the bandwidth information of thereceiving data.

In the fifth invention, because the propagation delay identifier used atbandwidth acquisition and the maximum transmission data size can be readfrom the outside through a transmitting medium, a different apparatusconnected to the same transmitting medium can get the acquired bandwidthand as a result, the procedure to acquire a bandwidth accompanied withbandwidth transition when a different transmitting apparatus transmitsusing the already acquired bandwidth can be simplified.

In the sixth invention, it is possible to effectively use the bandwidthwhich a transmitting medium has by that a transmission control apparatusanalyzes a connection topology of the apparatus connected to thetransmitting medium and set a propagation delay identifier based on theanalysis result. Further, because the propagation delay identifier canbe set from the outside of the apparatus through the transmittingmedium, it is possible to effectively use the bandwidth which thetransmitting medium has by that there is at least one transmissioncontrol apparatus on the transmitting medium, even not all transmittingapparatuses have analyzing means to analyze a connection form of theapparatus connected to the transmitting medium.

In the seventh invention, it is possible to effectively use thebandwidth without requiring any complex process by judging based on thenumber of apparatuses connected to the transmitting medium, when theconnection topology of the apparatuses connected to the transmittingmedium is analyzed.

In the eighth invention, a transmitting apparatus which is unnecessaryof an internal analysis of a digital signal can be gotten by countingthe data size and it is possible to reduce hardware and cost.

In the ninth invention, it is possible to control at a transmittingapparatus so that the buffer at the receiving apparatus side does notoverflow or under flow, by adjusting transmission timing. the number ofdata packets in the buffer in the receiving apparatus becomes maximum ina range it does not overflow by controlling so as to take as large valueas possible in a range not to exceed the fixed value as a counted valueand it is possible not to interrupt the output in the receivingapparatus as many as possible when some trouble occurs at thetransmitting apparatus or on the transmission medium and transmissionpackets do not arrive in the receiving apparatus for a certain period.

In the tenth invention, it is possible to output to a recordingapparatus at correct timing without overflowing of the buffer inside thereceiving apparatus, by that a transmitting apparatus adds atransmission time stamp indicating timing which a receiving apparatusoutputs to the data and transmits it and a receiving apparatus outputsat the timing written in the transmission time stamp.

What is claimed:
 1. Apparatus for transmitting data on a transmissionmedium comprising: overhead bandwidth including a size value of a timedelay related to a topology in a transmission medium, said overheadbandwidth being shown by using ID and determining the value by referringto a table chart; propagation delay identifier storage means for storinga propagation delay identifier which is used for bandwidth allocation;maximum data size storage means for storing a maximum data size valuewhich corresponds to maximum size of data included in a packettransmitted on said transmission medium; and a pathway coupled betweena) a further apparatus and b) said propagation delay identifier storagemeans and said maximum data size storage means so that said propagationdelay identifier and said maximum data size value are both readable by afurther apparatus.